In air-conditioning industry, textile ducts are used especially for air distribution, i.e. in rooms, for which the air is intended. Contrarily, metallic ducts are used to transport air towards the respective rooms, the metallic ducts being however substantially heavier, more expensive, more space-consuming and more difficult to clean in comparison to the textile ducts. Alternatively, textile ducts can also be used for conveying air provided that the textile material is imperviously coated, e.g. with PVC, in order to prevent air from being lost while being conveyed. Nevertheless, when cooled air is conveyed through rooms/areas, where high temperatures and/or humidity prevail, condensation occurs on the surface of such ducts causing condensate to drip down therefrom.
This problem can be solved by wrapping an insulating material around the entire duct. This is, however, uneconomic both with regard to the manufacturing cost and with regard to the maintenance cost. Moreover, the weight of the duct becomes significantly higher.
In accordance with U.S. Pat. No. 7,442,121, the aforesaid problem is solved by providing a duct that comprises an inner air-pervious layer, an outer impervious layer and multiple braces arranged between the two layers. The supplied air flows along the inner air-pervious layer of the duct but partly passes through that layer into the space between the inner and outer layers, thus forming an insulation that reduces the risk related to the occurrence of condensation on the outer surface of the duct. The drawbacks of the aforesaid technical solution consist in the complexity of the same and in an insufficient flexibility with regard to adjustment of the air permeability of the inner layer of the duct. In addition to that, the air permeability of said layer spontaneously fluctuates during the operation which is due to the fact that the pores of the textile material gradually become clogged by the impurities contained in the supplied air. Another drawback consists in that the supplied air penetrates the insulating layer along the entire length of the duct, thereby having a temperature, which is similar to that prevailing inside the duct, along the entire length of the duct. In view of the fact that, according to the prior art document, air from the insulating chamber is to be fed to the place of distribution, connection of such duct to an air diffuser is complicated from structural point of view.